The invention relates to a photoluminescent granulate consisting of a hardened mixture that includes a transparent, light-fast matrix that contains at least one photoluminescent luminous pigment and one transparent filler.
Effect pigments from the field of photoluminescence are used in various fields of application, e.g., in functional, decorative or safety fields. The high intrinsic function of these pigments and the changed requirements in the processing and application of these pigments resulting therefrom lead to the most varied technical requirements. Basically, these pigments must be metered to a greater extent compared with standard color pigments and can likewise be mixed with standard color pigments and/or solids but with high losses in the resulting luminance. Use in transparent, filler-less systems such as e.g., clear varnish, pure luminescent paints, transparent resin systems, is relatively simple to implement, but this is not readily possible in systems containing fillers.
The discussed systems that contain fillers are e.g., solid surface mineral material plates such as e.g., those known by the trademark “Corian®”, or so-called engineered stone materials. Solid surface materials are mostly a cast mixture of acrylic resins or polyester resins and a high proportion, typically greater than 50%, of e.g., aluminum trihydrate (ATH or Al(OH)3). Engineered stone plates are terrazzo-like or polymer concrete-like resin-bonded systems containing mineral fillers as are also typical in standard concrete goods, such as quartz, marble, chips, etc. The wall thicknesses of these materials is typically about 8 mm. In the field of solid surface plates, a standard thickness of about 12.5 mm has been established.
The properties of these materials are determined by the ratios of resin-binders (matrix) to filler, i.e., the filler is a core component of the definition of these products or of the properties of these products such as e.g., the B1 fire class rating of solid surface plates.
The conclusion drawn from this is that photoluminescent variants of these materials likewise have to contain a high proportion of corresponding fillers.
Essentially, there is the possibility of effecting a so-called “through-coloring” of the materials. In this method, a high proportion of pigment is used that completely penetrates through the plate or the material. However, this method has the disadvantage that on the one hand high costs are generated since extremely high material costs are generated owing to the thickness of the plates or layers and the low translucency of the fillers coupled with high pigment costs in the field of photoluminescent pigments. On the other hand, the pigments from deeper layers can no longer contribute towards the desired luminous effect owing to the excitation that is either too low or is absent. However, the proportion of pigment cannot be increased at will without greatly negatively influencing the material properties from a certain point.
In general, photoluminescent pigments also cannot be used very effectively in darker materials since the darker the surroundings of the pigments, the more greatly the luminous effect is absorbed. This results in a sharp decrease in the luminous effect.
One solution could be to provide granulates that could then be introduced into the plate material in the form of fragments of different sizes. The density of these fragments should then be adjusted such that during production they either fall or rise, in each case in the direction of the subsequent (visible) surface of the produced plate. This would result in the fact that these materials would represent only an extremely small proportion in the produced plate material and consequently would only have to be used in small quantities compared with previous processes.
The simplest manner of achieving this would be to embed the pigment into a synthetic material matrix and use this as a granulate in the various applications.
However, this is not readily possible for various reasons. On the one hand, the applications place different requirements on the particulate aggregates (granulates) in each case and on the other hand the fillers influence the photoluminescence of the pigments.
This is to be illustrated in the following example (Corian®):
Plates and molded parts having aluminum hydroxide as a filler, that are known for example under the trademark Corian®, enjoy increasing popularity. In this case, the casting compounds used for production are filled with colored particles of a size ranging from 0.1 mm to several millimeters. In order to allow these particles to become visible, and to increase the attractiveness, the plates are ground at the surface after production (hardening) in order to expose the particles (to a greater extent).
In order to ensure that the particles are deposited at the surface of the plates and molded parts, the added colored particles must have a density that corresponds at least to the density of the used dispersion of polymerizable binder and aluminum hydroxide. Depending upon the filler concentration, a density of 1.6 to 1.8 g/cm3 is thus desirable.
However, this density would have to be achieved without reducing the photoluminescence of the pigments if photoluminescent pigments are to be used in these products.
However, the density of the binders is only approximately 1.2 g/cm3. In order to achieve the desired density, additional fillers are thus required as is known.
Typically, these fillers should have a density that is as high as possible and a large particle size in order to achieve a transparency that is as high as possible.
For instance, a maximum luminance of the photoluminescent pigments should be obtained at the surface after grinding. Only those fillers having a low Mohs hardness are used as fillers in the present Corian® application used by way of example, owing to the required simple processing.
The fillers that are thus to be used must, however, also have a good connection with the binder used but do not have to disintegrate during processing.
For this reason, polyesters or acrylates modified by thermosetting are preferably used. A predominant portion of the colored particles used is produced from polyester. For this purpose, colored plates are produced using the pigments and fillers and are separated in subsequent comminuting and screening processes.
The granulate thus obtained is in turn used in the production of Corian® parts.
In contrast, in applications such as concrete stone or engineered stone, the decisive factor is the embedding of the pigment in a transparent matrix that has an extremely low expansion coefficient. This must also be achieved without a reduction in photoluminescence occurring.
In applications in which the resin system is in the background, as is the case in GRP, acrylic plates or resin molded parts of different types, i.e., in which the granulate is introduced into a resin system, the density must be adjusted close to the carrier medium in order to retain the produced fragments evenly in the system until hardening. Floating or sinking can be adjusted as required when the application requires it.
DE 197 49 234 A1 discloses highly-filled synthetic materials based on poly(methyl methacrylate), starting from a polymer precursor PVS consisting of methyl methacrylate and a poly(methyl methacrylate)-prepolymer that is converted into a filler suspension by adding at least one particulate inorganic filler in proportions of 30 to 80 wt. % (based on the filler suspension) with stirring at high speed, and that is polymerized by adding at least one radical initiator in a suitable form after the casting process, wherein a differently-colored, filled, ground polymer material is added to the filler suspension in amounts of 1 to 20 parts by weight (based on the filler suspension) with stirring with the proviso that the density of the ground material GP is precisely matched to the density of the filler suspension and that the polymeric component of the ground material is highly cross-linked, wherein the highly-filled synthetic material contains at least one luminescent pigment on an inorganic basis.
US 2006/0038161 A1 discloses a phosphorescent, thermosetting, acrylic-based mixture in which fillers are not used for transparent products (cf. paragraph [0027]). In contrast, in the case of opaque products, fillers such as aluminum hydroxide are used (cf. paragraph [0029]). The typical alkali or earth alkali metal aluminates are used as pigments (cf. paragraph [0024]).